Axial-flow machines



Sept. 18, 1956 w. H. LINDSEY AXIAL-FLOW MACHINES Filed Sept. 22, 1950 u a A M f l V F- 2 m w z M @W M m w w 7 4 U a 2 1M J MG \B llll llllll f-fi x s -IHHHHHHH 2 5 F, n w H m M m I M u m.

AXIAL-FLOW MACHINES William H. Lindsey, Coventry, England, assignor to Armstrong Siddeley Motors Limited, Coventry, England Application September 22, 1950, Serial N 0. 186,268

Claims priority, application Great Britain ()ctober 13, 1949 3 Claims. (Cl. 230-122) This invention relates to an axial-flow bladed compressor, particularly for a gas turbine unit.

It is well known that the air velocity at the inlet of such a compressor should be as uniform as possible over the whole area of the inlet, as otherwise there is the possibility of resonance effects occurring in some of the rotor blades and the consequent risk of fracture of the latter. This possibility is more pronounced when the entry to the compressor is obstructed by members forming a structural part of the entry, for example, supporting webs of substantially streamline section extending radially across the annular intake duct. The existence of such webs produces wakes at the trailing edges which obviously interfere with the uniform velocity flow into the compressor.

It is therefore the main object of the invention to eliminate such wakes in a very simple and satisfactory manner; and, accordingly, air is supplied under pressure to the interior of a web and is ejected from or near the trailing edge at a relatively high velocity into the zone where a wake might otherwise form. This tends to produce an ejector effect, so that air passing over and near the surface adjacent the trailing edge, which would otherwise eddy and promote wake formation, is entrained and mixed with the high velocity air so as to promote streamline flow and inhibit wake formation, and it also acts to re-energise any wake that may form.

Although a single aperture in the form of a slit along the whole of the trailing edge of a web is theoretically possible, and desirable, the width of such a slit would be so small as to be impractical, and it is therefore preferred to provide in the trailing edge of a web, along the radial length thereof, a series of small holes communicating with a duct or chamber in the interior of the web, the holes supplying a metered quantity of air from the compressor outlet. In practice it is not really convenient for the holes themselves to be metered holes, and the supply to the said duct or chamber may therefore be a metered one.

Alternatively, a series of metered holes, or holes supplied from a metered orifice, along the surface of a web adjacent the trailing edge and communicating with an internal pressure-fed duct or chamber could be used, the position of the holes relatively to the trailing edge being determined experimentally.

In the accompanying rather diagrammatic drawings:

Figure 1 is an elevation of a gas turbine unit, with an enclosing casing shown in section, arranged according to the invention;

Figure 2 is a fragmentary sectional elevation of the front end thereof to a larger scale, showing two of the webs in the compressor intake duct; and

Figure 3 is a fragmentary sectional elevation, to a still larger scale, of one of these webs, Figure 4 being a crosssection taken upon the line 44 of Figure 3.

The drawings show a gas turbine unit comprising an axial-flow bladed compressor 11, combustion equipment 12, in which the output from the compressor is heated by States Patent ice the addition thereto of fuel, and a turbine 13 driven by the output from the combustion equipment and driving the rotor of the compressor, and, in addition, exhausting along a jet pipe 14.

Figure 2 indicates, at 16, one of the blades of the first stationary row of compressor blades, and at 17 one of the blades of the second stationary row of the compressor blades, Whilst 18 and 19 respectively represent blades in the first and second rows of compressor blades which are fast with the compressor rotor 20. The latter is shown as being fast with a shaft 21 which is journalled at 22 in a stationary frame member 23 fast with one of the webs 24. It is assumed that there are four webs 24, extending radially across the intake duct, which are spaced at 90 from one another and which interconnect an inner sta tionary frame structure 25 and an outer stationary casing 26, the leading edge of which latter is shown as extending up to the forward edge of a streamline casing 27 enclosing the main portion of the gas turbine unit.

Figures 1 and 2 show a pipe 29 which picks up air from the outlet end of the compresor, for example, from the inlet manifold, indicated at 30, of the combustion equipment 12, and delivers it forwardly to a radial passage 31 in one of the webs 24, the inner end of the passage 31 communicating by means of a duct 32 (Figure 3) with an annular chamber 33. The latter communicates with each of the radial passages 34, near the trailing edge of a web 24, through a metered hole 35, and the trailing edge of each web is provided with a plurality of small parallel holes 36 (shown of exaggerated bore in Figures 3 and 4) through which the metered quantity of air supplied to the passage 34 can escape substantially uniformly from the trailing edge of the web.

The mass flow of air for this purpose, and its speed of ejection from the holes 36, will, of course, depend upon the characteristics of the gas turbine unit. They may be easily calculated and ascertained by experiment. In the case of an engine having an operating power range of between, say, 4,500 R. P. M. and 8,000 R. P. M., it may be found, for example, that it is at a speed of about 5,000 R. P. M. that failures in the compressor are most likely to occur. To counteract this (i. e., to prevent wake formation), it is satisfactory, in one instance, for each of the holes 36 to have a diameter of about 0.052" (0.132 cm.) and for the metering hole 35 to have a diameter of about 0.199" (0.505 cm.) to give, say, a jet velocity from the holes 36 of approximately 500 per second (152 metres/ sec.) with a supply pressure from the compressor outlet of, say, approximately two atmospheres absolute. The mass flow of bled air to each web, in these conditions, may be approximately 0.06% of the mass flow through the compressorthe velocity of such mass flow past the webs being about per second (48.8 metres per second).

The holes 36 are spaced along the trailing edge of each web 24 to simulate the effect, at a short distance downstream of the trailing edge, of a slit along this edge, which would theoretically be an ideal arrangement-i, e., the exit velocity of the bled air would become substantially constant along the whole radial length of the web.

If it were practicable to arrange the holes 36 as metered holes, thus obviating the use of the metered hole 35, then these holes 36, in the conditions above-mentioned, might have a diameter of about 0.035" (0.089 cm.), giving a jet velocity of approximately 650' per second (198 metres/see); but, as stated, provision of a series of metered holes 36 in each web is not satisfactory from a practical point of view, in consequence of which the arrangement shown in the drawings, where "there is only one metered hole 35 for each web, is preferred.

With the arrangement shown in the drawings a greater percentage of compressor mass flow per web may have "webs h 3 to bebled-than when all the holes 36 are metered holes i. e., about 0.06% instead of about 0.02%but this is still a relatively negligible amount.

All this applies to an assumed rotor speed of about 5,000 R. P.- M. for one'partic'u'lar gastur-bine unit; but at highe'rrotor speeds the quantity of air bled from the compressor is still quite negligible.

It should be borne in mind that, with the arrangement shown in the drawings, it is asi'r'nple matter to remove any of the metered jets'35, as will be evident from a considera- "tion of Figure -3, and to open the bore'therein, or to replaceit by a smaller jet, should either operation be found to bed'esirable.

7 What I claim as myinvention and desire to secureby Letters Patent of the United States is:

-1.' Ah axial-flow bladed compressor including inner and outer stator parts providing "an intake duct, radiallyxt'ending webs interconnecting said parts adjacently upstream of a "first blade row er said compressor, each of said'webs of strea'm-line cross-section and having in 'it a passage communicating witha line of small holes along the trailing edge of the web,- one of said parts having an annular ehamber'in it connected with each of saidpassages through a meteredhole, and means providing a passa eway interconnecting the outlet end of said compressor and said annular chamber, said metered holes being of "such a diameter as 'to control the velocity of the air issuing from 'saidsmall holes so as'to be higher than thatof the'air passing'through said du'ct externally of said webs.

2. "An axial-flowbladed Compressor including-innerand 'out'er'stator parts providing an intake duct, webs of streamlined section adjaee'ntly"upstram of"a"first-blade row of said c inpressor and extendingacross said duct, "said ingbutlts n'ear their tr'ailirig edges and communicatin'g'with the interiors 'of the 'webs,'and means providing a passage-way from the ounerena of said-compressor "for-supplying air "under: pressure to the interior -of each of 'said" webs,- said' mans including mtered holes of such diameter that the air passing therethrough will be ejected from said outlets in the downstream direction at a higher velocity than that of the air passing through said duct externally of said webs whereby to prevent the air which passes through said duct externally of said webs from forming wakes downstream of the latter.

3. An axial-flow bladed compressor including inner and outer stator parts providing an intake duct, webs of streamlined section adjacently upstream of a first blade row of said compressor and extending radially across said duct, a passage in the interior of each said web, each said passage provided with a metered hole, said web provided along the radial length of their trailing edges with a series of small holes communicating with the metered hole, and means providing a passage-way from the outlet end of said compressor for supplying air under pressure to the interior passages of said webs and through said metered holes, said metered holes being of such diameter as to eject the air through'said small holes at a higher velocity than that of theair passing through said duct externally of said webs whereby to prevent the air which passes through said duct externally of said webs from forming Wakes downstream of the latter.

References Cited in-the-file of this patent UNITED STATES PATENTS Re..23,-108 vStalker May 3, 1949 2,406,473 Palmatier 1 Aug. 27,1946 2,469,375 Flagle May 10, 1949 2,527,971 .Stalker Oct. 31, 1950 2,625,010 .Clark Jan. 13,1953 2,636,666 .Lombard Apr. 28, 1953 FOREIGN PATENTS 225, 232 Switzerland Aprgl6, 1943 618,224 iGreatBritain Feb. 17, 1949 "619,390 GreatBritain Mar. 8, 1949 

